A liquid crystal display device is a plane display device which has excellent characteristics of being high-definition, thin, and light and realizing low power consumption. The market for the liquid crystal display device has recently been expanded rapidly along with improvement in display performance, production capacity, and price competitiveness over other display devices.
A conventionally common twisted nematic mode (TN mode) liquid crystal display device is subjected to an alignment treatment such that major axes of respective liquid crystal molecules having a positive dielectric anisotropy are aligned substantially parallel to a substrate surface so that the major axes are twisted by substantially 90° between upper and lower substrates along a thickness direction of a liquid crystal layer. Application of a voltage to the liquid crystal layer causes the liquid crystal molecules to rise parallel to an electric field, so that no twist alignment exists. The TN mode liquid crystal display device uses a change in optical rotation in response to a change in alignment of the liquid crystal molecules by voltage application, so as to control an amount of transmitted light.
The TN mode liquid crystal display device is excellent in productivity due to its wide production margin. In contrast, the TN mode liquid crystal display device has a problem about display performance, especially a viewing angle characteristic. Specifically, the TN mode liquid crystal display device has a problem such that a display contrast ratio is dramatically reduced when a display plane of the TN mode liquid crystal display device is obliquely observed and a luminance difference between gray scales is considerably indistinct when an image is obliquely observed such that a plurality of gray scales from black to white are distinctly observed when the image is observed from the front. The TN mode liquid crystal display device also has a problem about a phenomenon (a so-called gray scale reversal phenomenon) such that a gray scale characteristic of a display is reversed and a part which is darker when observed from the front is brighter when obliquely observed.
A liquid crystal display device which has been developed by improving a viewing angle characteristic of such a TN mode liquid crystal display device is exemplified by an IPS mode (in-plane switching mode) liquid crystal display device, an MVA mode (multi-domain vertically-aligned mode) liquid crystal display device, and a CPA (Continuous Pinwheel Alignment) mode liquid crystal display device.
Each of these new mode (broad viewing angle mode) liquid crystal display devices solves the specific problems described above about a viewing angle characteristic. Namely, there occurs no problem such that (i) a display contrast ratio is dramatically reduced when a display plane is obliquely observed and (ii) a display gray scale is reversed.
However, as a display quality of a liquid crystal display device improves, a new problem about a viewing angle characteristic is growing more evident. The new problem is a phenomenon such that a γ characteristic is different between when a display plane is observed from the front and when the display plane is obliquely observed, i.e., a problem of a viewing angle dependence of the γ characteristic (e.g., excess brightness). Note here that the γ characteristic is a gray scale dependence of a display luminance. The phenomenon such that the γ characteristic is different between when the display plane is observed from the front and when the display plane is obliquely observed causes a gray scale display state to differ depending on an observation direction. Therefore, such a phenomenon causes a problem especially in a case where an image such as a photograph is displayed or in a case where a TV broadcast or the like is displayed.
The problem of the viewing angle dependence of the γ characteristic is more noticeable in the MVA mode and the CPA mode than in the IPS mode. In contrast, it is more difficult in the IPS mode than in the MVA mode and the CPA mode to produce, with high productivity, a panel which has a high contrast ratio when observed from the front. In view of these points, especially the MVA mode liquid crystal display device and the CPA mode liquid crystal display device are desired to improve in viewing angle dependence of the γ characteristic.
Patent Literature 1 discloses a liquid crystal display device which includes an image processing section in which a high luminance frame and a low luminance frame are combined. In the high luminance frame, each pixel is driven at a higher luminance than a specified luminance corresponding to a gray scale value of input image data. In the low luminance frame, the each pixel is driven at a lower luminance than the specified luminance. In order to obtain a luminance which is substantially equal to the specified luminance, the image processing section determines a luminance (a bright luminance) at which the each pixel is driven in the high luminance frame and a luminance (a dark luminance) at which the each pixel is driven in the low luminance frame, and a ratio of the high luminance frame to the low luminance frame. According to this liquid crystal display device, which carries out so-called time-division driving with respect to the each pixel, an average value of a brighter bright luminance and a darker dark luminance is displayed as an intermediate luminance. This reduces occurrence of excess brightness due to the intermediate luminance and consequently can improve the viewing angle dependence of the γ characteristic.